The present invention relates to a magnetic disk apparatus and, more particularly, to a magnetic disk apparatus of a large capacity in which a recording density in a radial direction is increased.
Typical examples of a magnetic disk apparatus and a magnetic head suspension which have been hitherto put into practical use are disclosed in JP-A-55-22296. In the foregoing prior art, the suspension consists of a loading arm and a gimbal. A slider on which a magnetic head is mounted is fixed to the gimbal by adhering or the like. A projection called a dimple is provided for the gimbal or a front edge portion of the loading arm, and the slider can be freely rotated in an outer direction of a disk surface by setting a top of the dimple as a supporting point. The loading arm has a spring portion on the side of a supporting arm so that the slider can trace the disk surface, thereby allowing a flexible structure to be provided in the vertical direction of a disk surface. In order to apply a predetermined load to the slider, the spring portion of the loading arm is bent along the width direction and is attached thereto, so that the loading arm and disk surface are set to an almost parallel state to thereby apply a load to the slider.
In the magnetic disk apparatus of a disk diameter of, particularly, 5.25" or less, in order to miniaturize a size of the apparatus and reduce an inertial mass upon accessing, there is ordinarily used an in-line system for arranging the supporting arm and suspension in line and positioning the supporting arm onto a predetermined track by rotating.
In the magnetic disk apparatus, in order to realize a large capacity, the number of tracks in the radial direction increases year after year and positioning precision becomes ever more important in accordance with the increase. However, a positioning error (hereinbelow, referred to as a flutter error) due to deflection fluctuation (hereinbelow, referred to as flutter) in the disk, tends to occur with the increase in the number of tracks. This creates a problem that an adverse influence is exerted on positioning precision.
A mechanism of the flutter error will now be described hereinbelow with reference to a low fluctuation mode having no circular segment which is an actual problem.
When flutter occurs, a deflection as a displacement in the disk surface outer direction and a deflection angle in the radial direction of the disk surface simultaneously occur. When the disk is curved on the slider side by the deflection angle, tracks on the disk surface are deviated on the inner peripheral side. For example, in the prior art as mentioned above, the suspension is flexible in the vertical direction of the disk in a still state and is rigid in the radial direction. Therefore, the top of the dimple moves on a line in the vertical direction of the disk in the still state. Since the slider rotates at the top of the dimple as a center, a read/write gap (hereinbelow, referred to as a gap) of the magnetic head located on the disk surface side of the slider is deviated on the outer peripheral side when the disk is curved on the slider side. As for the above-mentioned phenomenon, when the disk is curved on the side opposite to the slider as well, the deviations of the tracks and gap occur in the similar mechanism, though the directions to be deviated are opposite. That is, when the disk is curved on the slider side, the tracks are deviated on the inner peripheral side and the gap is curved on the outer peripheral side. When the disk is curved on the side opposite to the slider, the tracks are curved on the outer peripheral side and the gap is deviated on the inner peripheral side. The sum of the deviations of the tracks and gap appear as a flutter error.
As seen in Seo et al., "Analysis of Head Positioning Error Caused by Disk Surface Flutter", Integrated National Convention of The Institute of Electronics and Communication Engineers of Japan, 1984 or Gill Bouchard et al., "Non-Repeatable Flutter of Magnetic Recording Disks", IEEE Transactions on Magnetics, Sept., 1986, a generation mechanism of the flutter error has been known but an effective solving method has not previously been proposed.